Contact assembly for switches

ABSTRACT

In a high voltage disconnect electric switch, a rotatable switchblade is provided with a contact portion at one end having an edge which is adapted to remain coincident with the axis of rotation of the switchblade throughout the blades rotation. A stationary terminal is maintained in continuous electrical contact with this blade edge. A rotatable contact assembly is also provided receivable of the switchblade and includes a contact portion having an edge adapted to remain coincident with the assembly&#39;&#39;s axis of rotation. Another stationary terminal is maintained in continuous electrical contact with this contact edge. Both the blade and the contact assembly remain in static contact with respective terminals throughout the rotation of the various members thereby reducing wear and other associated problems.

Linde CONTACT ASSEMBLY FOR SWITCHES [451 July 17, 1973 PrimaryExaminerDavid Smith, Jr.

75 Inventor: Leonard J. Linde, Brookfield, Wis. Mmiime [73] Assignee:Gulton Industries Inc., Metuchen,

NJ. [57] ABSTRACT [22] Filed: Aug. 11, 1972 in a high voltage disconnectelectric switch, a rotatable I L N 279 50 Switchblade is provided with acontact portion at one [2 1 App ,8 end having an edge which is adaptedto remain coincident with the axis of rotation of the switchblade US. Cl00/170 A, 200/48 K 200/l46 R, throughout the blades rotation. Astationary terminal is O /1 ZOO/166 BF maintained in continuouselectrical contact with this [51] Int. Cl. H0lh 1/50, HOlh 9/60 bl d d Arotatable contact assembly is also prol Fifild 0f Search 200/48 48 KB,vided receivable of the Switchblade and includes a con- 200/l7O 166 146R tact portion having an edge adapted to remain coincident with theassemblys axis of rotation. Another stal l Referenctis Cited tionaryterminal is maintained in continuous electrical UNITED STATES PATENTSContact with this contact edge. Both the blade and the 1 238 597 8/1917Terzich 200/162 assembly remain in Static with respec- 2I239I224 4/1941Goldmer 200/146 R tive terminals throughout the rotation of the various2,241,810 5/1941 Dickinson 200/162 members thereby reducing wear andother associated 2,714,646 8/1955 Jamison 200/48 KB problems. 3,671,6896/l972 Falvo 200/170 A Claims, 6 Drawing Figures I 0 I l '24 ,4- .4 2227 48 (Pao 40 II II 26 Pat ented July 17, 1973 I 3,746,819

3 Sheets-Sheet 1 Pa te'nted July 17, 1973 3 Sheets-Sheet 2 FIG. 4

r Patented July 17 1973 Sheets-Sheet :5

FIG. 6 l

CONTACT ASSEMBLY FOR SWITCHES BACKGROUND OF THE INVENTION This inventionrelates generally to high voltage electric switches, and moreparticularly to contact assemblies for reducing contact wear andoperating effort required to operate high voltage switches employingmembers rotating in a single plane.

High voltage disconnect-type electric switches often comprise a pair ofspaced stationary terminals mounted on the top of insulator stacks witha pivotally mounted switchblade which electrically interconnects the twoterminals when the switch is closed. The switchblade is pivoted out ofmutual electrical engagement with the terminals when the switch is open.

In many of these switches, the pivotal switchblade is continuouslyelectrically connected to one of the terminals whether the switch isopen or closed. This feature has proven to be convenient since theswitchblade need only be moved into and out of engagement with thesecond terminal to close and open the switch.

In the past, however, problems have arisen from attempts to provide botha reliable mechanical pivotal connection and continuous electricalengagement between the movable switchblade and the terminals. Forexample, flexible electrical conductors have been used to continuouslyelectrically connect a terminal to the adjacent end of the pivotableswitchblade, These flexible connectors, however, have been found to besubject to wear and, when repeatedly flexed over a period of time, haveoften failed. A second arrangement finding common use includes pivotallymounting the switchblade directly to the terminal on an electricallyconductive shaft. In these arrangements, the switchblade surfacecontinuously rubs against the terminal contact surface during theopening and closing of the switch mechanism, producing wear which makeselectrical contact unreliable. These arrangements have also provensusceptible to corrosion and pitting along the electrically conductivesurfaces over extended periods of time and have proven unreliable forthis reason also. Further, high voltage switches occasionally conducthigh fault currents which are generated due to inadvertent shortcircuits and other circuit malfunctions. These fault currents havecaused deformation of the electrically con- SUMMARY OF THE INVENTIONAccordingly, one object of this invention is to provide new and improvedcontact assemblies for electrical switches.

Another object of the invention is the provision of a new and improvedcontact assembly which will not become unduly worn after extendedperiods of use.

A further object of the invention is to provide a new and improvedcontact assembly which will continue to operate despite high faultcurrents;

A still further object of this invention is the provision of a new andimproved switch mechanism which has increased icebreaking capability.

Another still further object of the instant invention is the provisionof a new and improved continuous contact assembly which will reduce theoperating effort in opening a switch.

Briefly, in accordance with a preferred embodiment of the invention,these and other objects are attained by providing an electric switch inwhich the pivotally mounted switchblade is provided with a contactportion having an edge coincident with the axis of rotation of theswitchblade. A stationary terminal is in continuous electricalengagement with this contact edge during the rotation of theswitchblade. A rotatable contact assembly is provided for engagementwith the free end of the rotating switchblade and includes a contactportion which has an edge coincident with the axis of rotation of thiscontact assembly. A second stationary terminal is in continuouselectrical engagement with this contact edge during rotation ofthecontact assembly. As the switchblade rotates into and out ofengagement with the contact assembly, the contact assembly is caused torotate along with the blade to reduce the operating forces which wouldotherwise be necessary to operate the switch. The free end of theswitchblade has a wiping effect on the contact assembly during theopening and closing of the switch which tends to clean the contactsurfaces and improve deicing capabilities.

DESCRIPTION OF THE DRAWINGS A more complete appreciation of theinventionwill be had by reference to the following detailed description whenconsidered with the accompanying drawings wherein:

FIG. 1 is a partial plan view of the stationary terminal and pivoted endof the switchblade;

FIG. 2 is a side view of the stationary terminal and switchblade of FIG.1 in a pivoted position;

FIG. 3 is a side view taken in section along line 33 in FIG. 1; r

FIG. 4 is a plan view of the pivotal contact assembly of the presentinvention; a a

FIG. 5 is a side view of the pivotal contact assembly of the presentinvention; and

FIG. 6 is a view in section taken along line 6- 6 in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingswhere like reference characters designate identical or correspondingparts throughout the several views and, in particular to FIGS. 13, aswitchblade I0 is illustrated as pivotally mounted on the upper end ofan insulator stack 12. As best seen in FIG. 1, switchblade I0 isbifurcated at its end to form a pair of legs 14 having a respectivepair. of aligned bores 16 formed therein. EAch bore 16 is also alignedwith a bore 18 (FIG. 1) formed in a pair of arms 19 extending from a cap20 fixed to the upper end of the insulatorstack 12. A pivot 22 is passedthrough each set of aligned bores and, in the present embodiment, eachpivot has a threaded shankportion which is received by internallythreaded bore 18 which thereby retains the pivot 22 in position. Themounting structure is only representative of one of a number ofconfigurations possible within the scope of the present invention.

A contact portion 26 is fixed to the switchblade end 24 by conventionalmeans such, for example, as by bolts 28 (FIG. 3). Contact portion 26comprises an elongate bar formed of an electrically conductive materialwhich is suitably treated to insure high surface conductivity and has asubstantially rectangular cross section with its lower surfacesubstantially coplanar with the lower surface of switchblade 10. As bestseen in FIG. 3, the upper surface 27 of the contact portion 26 extendsfrom the approximate midway point of the height of switchblade end 24and intersects the rear surface 29 of the contact portion at edge 30. Inthe present embodiment, the surfaces 27 and 29 meet at the edge 30 at anangle of slightly less than 90 so that rotation of the switchblade canbe accomplished as described below without danger of interferencebetween contact portion 26 and various contacts. As best seen in FIG. 2,the axis of rotation of the switchblade (which is merely the axes of thepivots 22), is precisely colinear with the edge 30 of contact portion26. Thus, when switchblade 10 is rotated about the pivots 22, the edge30 of contact portion 26 virtually remains static along the axis ofrotation of the switchblade, with at most a slight wiping action.

One means by which the switchblade may be rotated is shown in FIG. 1 andincludes a push-pull rod 32 connected to an extension 33 of switchblade10 through a universal joint 34. A pair of compression springs 36 (onlyone shown) are provided on associated shafts 37 which shafts arepivotally mounted at their ends to extension 33 biasing the switchbladetowards its closed position as shown in FIG. 1. Thus, should it bedesired to open the switch, push-pull rod 32 is moved towards the rightthereby pivoting the switchblade 10 around its axis of rotation (definedby pivots 22) against the force of springs 36. As described above, asthis rotation progresses, the edge 30 of the contact portion 26 remainssubstantially stationary coincident with the axis of rotation. Othermeans for actuating the switchblade are known in the art and may beemployed in lieu of the structure described above.

A plurality of U-shaped or loop contact members 38 comprising astationary terminal are fastened to cap 20 by conventional fastenerssuch, for example, as by bolts 40. The cap 20 is provided with ahorizontal ledge 42 upon which rests the end of a bus bar 44 whichcarries current to the loop contacts 38. One of the legs of eachterminal contact 38 is bent at right angles to itself and is sandwichedbetween a cover plate 47 and the upper surface of the end of the bus bar44 thereby electrically engaging the bus bar.

Referring to FIG. 3, the free leg 45 of each terminal contact 38 isurged against the edge 30 of the contact portion 26 by a compressionspring 46 which is interposed between the two legs of each contactmember. Thus, the plane of the contact surface of each terminal contactcontains the axis of rotation of the switchblade ID at the line ofcontact with edge 30. Since springs 46 are normally compressed, a highcontact pressure is maintained between the free leg of each loopterminal contact and the contact portion edge 30 so that when theswitchblade 10 is rotated from its closed to its open position bysuitable actuation of rod 32. Electrical connection is maintainedbetween the terminal contact 38 and the contact portion 26 of theswitchblade.

The extent of rotation of the switchblade I0 is limited by a stopsurface 48 formed on either or both of the legs 14. As shown in FIG. 3,the stop surface 48 is vertically oriented (when the switch is closed)so that upon rotating the switchblade 90 from the position shown in FIG.3, the surface 48 will engage the cover plate 47 thereby preventing anyfurther rotation.

Thus, the electrical connection between the terminal contacts 38 and theswitchblade 10 is continuously maintained by virtue of the coincidentrelationship of the edge 30 and the axis of rotation of the switchbladewith the free leg of each fixed terminal loop contact 38 bearing againstthe blade edge 30. The disadvantages of the continually bending,flexible, electrical connectors and those due to rubbing contact betweenelectrically conductive surfaces are eliminated. Further, by using theterminal loop contacts 38, a constant magnetic field is produced by thecurrent passing through the loop contacts 38 when the switch is closed.Such a magnetic field serves to increase contact pressure with contactportion 26 in a manner well-known in the art. This is especially trueduring operation under high fault currents.

Turning now to FIGS. 4, 5 and 6, a contact assembly 50 is illustratedwhich receives the free end 52 of a pivotal switchblade when theswitchblade is moved to' close the switch mechanism. It should beunderstood that, although this contact assembly 50 may be used inconjunction with the contact structure disclosed relative to FIGS. 1-3,such conjoint use is not necessary. That is, the contact assembly 50described below' may be used in conjunction with other prior artswitches within the scope of the present invention.

The contact assembly 50 is mounted on a cap 56 fastened by bolts 57 tothe upper end of an insulator stack 54.

The contact assembly 50 comprises a generally U- shaped frame defined bya pair of parallel extending arms 58 and 60 connected by a bridgingmember 62 which is formed of an electrically conductive material. Aplurality of loop contacts 64 are fastened to the inwardly facingsurfaces of the arms 58 and 60. In the preferred embodiment, the loopcontacts are fastened to the frame by elongating one leg of each loopcontact and fixing these legs between the bridging member 62 and therespective parallel arms 58 and 60 by bolts 66. Thus, there is constantelectrical connection between the bridging member 62 and the loopcontacts 64.

In a manner similar to cap 20, cap 56 is formed with a pair of upwardlyextending arms 68, each having a bore (FIG. 4) formed therein alignedalong the same axis. The lower arm 60 is formed with a pair of upwardlyprojecting legs 72 which include bores 74 alignable with bores 70 whenthe legs 72 are suitably positioned between arms 68 as best seen in FIG.4. The contactassembly 50 is pivotally mounted on cap 56 by a pair ofbolts 76 having partially threaded shanks passing through the pair ofbores 74 and 70. Bores 70 are interiorly threaded while the innerportion of the shanks of bolts 76 are similarly threaded so that bolts76 may be fixedly maintained within the aligned bores. This mountingstructure is only one of a number of possible structures which may beemployed.

The bridging member 62 of the contact assembly 50 is formed with arearwardly protruding portion 78 terminating at a horizontally extendingedge 80 (FIG. 6). Tl-Ie protruding portion 78 is formed in a manner thatthe edge 80 is made coincident with the axis of rotation of the contactassembly, i.e., the edge 80 lies along the axis of the aligned bores 70and 74 and bolts 76. Thus, as the contact assembly is rotated, the edge80 of the protruding portion 78 remains virtually stationary on the axisof rotation of the contact assembly.

A horizontally extending ledge 82 (FIG. 6) is formed on cap 56 andtraverses the width of the cap. This ledge supports a bus bar 84 whichwill conduct current when the switch is closed. A plurality of terminalloop contacts 86 are fixed to the upper surface of the bus bar 84 byconventional means, such as, for example, bolts 88 which fix a bentportion of one leg of each loop contact 86 onto the upper surface of thebus bar 84.

The free leg 87 of each terminal contact is maintained in continuousengagement with the edge 80 of the protruding portion 78' of thebridging member 62 under the force-of a compression spring 90 whichurges the legs of the terminal contacts apart thereby maintaining highcontact pressure between the free leg 87 of terminal contact 86 and edge80.

Thus, in operation as described below, as the contact assembly 50rotates, continuous contact is maintained between edge 80 of thebridging member 62 andthe terminal contacts 86. Further, such contact isvirtually static, i.e., the edge 80 and the surface of the terminalcontacts with which it is in contact essentially do not move relative toeach other during rotation of the contact assembly except for a slightrolling action. By virtueof this fact, similar advantages to thosediscussed above relative to the switchblade connection assembly areattained.

In operation, referring to FIGS. 5 and 6, a switchblade, pivoted at aremote end (not shown, but which may be as described relative to FIGS.1-3) which had been in a previously open position, is caused to pivotdownwardly with its end 52 approaching the contact assembly 50. Asshownin FIG. 5, switchblade end 52 is moving downwardly in the direction ofarrow 92. A compression spring 94 positioned over a rod 96 having oneend pivotally connected to leg 72 at apoint 98 and the other endslidably connected to cap 56 at point 100 normally maintains the contactassembly in the position shown in FIG. 5, i.e., in an upwardly pivotedposition. When the end 52 of the switchblade moves into engagement withthe contact assembly, it urges the assembly 50 downwardly against theforce of spring 94. As shown in FIG. 5, the loop contacts -64 disposedon the lower plate 60may extend slightly further than those disposed onthe upper plate 58. In the present embodiment the switchblade 52 isshown as comprising a pair of parallel blades 102 and 104 (FIG. 4)connected by bridgingbar 106 at the end. By virtue of this arrangement,the bridging bar 106 at the end of switchblade 52 willengagecontactassembly 50 along the loop contacts provided on lower arm60 without interfering with the loop contacts disposed on upper arm 58.

'As the switchblade 52 moves downwardly, ultimately reaching itshorizontal position as shown in FIG. 6, the contact assembly 50 pivotsin a clockwise direction denoted by arrow 108 in FIG. 5, and until arms58, 60 are horizontal. As explained above, continuous electricalengagement is maintained between the edge 80 of bridging plate 62 andthe terminal contact members 86 during the rotation of the contactassembly. The bridging bar 106 is in electrical connection with loopcontacts 64 at its upper and lower edges and, therefore, the

electrical connection between switchblade 52 and bus bar 84 is made.

The rotatability of contact assembly 50 facilitates the disconnectorswitch opening operation of the end of switchblade 52 from the contactassembly 50. Further, the scraping action of the end of the switchblade52 along the inner surfaces of the loop contacts 64 serves to break upany ice which may have formed on the contacts 64 while the switch was inits open position. The center-of-rotation contact feature provides areliable electrical connection between the contact assembly 50 and thebus bar 84 with all of the attendant advantages described with regard tothe assembly disclosed in FIGS. 1-3.

While a particular embodiment of the invention has been shown anddescribed, it will be obvious to those skilled in the art that variouschanges and modifications may be made-without departing from theinvention in its broader aspects, and it is therefore intended that theappended claims cover all such changes and modifications as fall withinthe scope of the invention.

What is claimed is:

1. An electric switch comprising, a movable electrical member mountedfor rotation around an axis of rotation, at least one stationaryterminal contact mountedso that a segment thereof lies substantiallyalong the axis of rotation of said movable member, said member having acontact portion formed on one end with an edge substantially coincidentwith the axis of rotationv of said member said edge electricallyengaging said stationary terminal contact segment.

2. The switch recited in claim 1, wherein the stationary terminalcontact includes a U-shaped contact comprisinga pair of contact legs,one of said legs in a plane passing through the axis of rotation of theswitchblade.

3. The switch described in claim 1, wherein the movable member contactportion includes an edge coincident with the axis of rotation of themember and continuously in contact with the segment of the terminalcontactwhich passes through said axis of rotation.

4. The switch recited in claim 1, wherein the stationary terminalcontact includes a U-shaped contact which includes a pair of contactlegs having a spring disposed therebetween normally urging the legsapart so that one of the legs is urged against said contact portion edgewhich is substantially coincident with the axis of rotation of themovable member.

5. The switch as recited in claim 1, wherein the stationary terminalcontact includes a plurality of U- shaped terminal contacts, eachcontact member having a leg which substantially passes through thecenter of rotation of the'movable member.

- 6. The switch as recited in claim 1, wherein the contact portion isformed of an electrically conductive material rigidly connected to themember having an edge defined by a pair of surfaces meeting at an angleof or less, the edge being substantially coincident with the axis ofrotation of the member.

7. The switch of claim 1, wherein one end of the movable member isbifurcated to form a pair of spaced legs and the contact portion of themovable member includes an electrically conductive block rigidlyconnected to the member, the block extending within the space betweenthe legs substantially from one leg to the other.

8. A switch terminal contact assembly comprising a contact assemblymounted for rotation about an axis of rotation, a contact portion formedon the contact assembly having an edge adapted to remain substantiallycoincident with the axis of rotation of the contact assembly duringrotation thereof, and at least one stationary terminal contact membermounted so that a segment thereof passes through the axis of rotation ofthe contact assembly.

9. The terminal assembly recited in claim 8, wherein the terminalcontact member includes a U-shaped contact comprising a pair of contactlegs, one of said legs passing through the axis of rotation of thecontact assembly.

10. The terminal assembly recited in claim 8, wherein the contactassembly contact portion includes a projection having an edge coincidentwith the assembly axis of rotation and continuously inelectricalengagement with the segment of the stationary contact member whichpasses through the assembly axis of rotation.

11. The terminal assembly recited in claim 8, wherein the stationaryterminal contact member includes a U- shaped contact formed of a pair ofcontact legs having a spring disposed therebetween normally urging thelegs apart so that one of the legs is urged against said edge of thecontact assembly contact portion which is substantially coincident withthe axis of rotation of the switchblade.

12. The terminal assembly defined in claim 8, wherein the contactassembly has a substantially U- shaped frame and includes a pair ofspaced parallel arms connected by an electrically conductive bridgingmember, the parallel arms having mutually opposed electrical contactsfixed thereon and the bridging member having a rearwardly extendingprojection formed thereon terminating in said edge which issubstantially coincident with the center of rotation of the contactassembly.

13. The terminal assembly as defined in claim 8, wherein a pair ofspaced arms are provided on the contact assembly and the contactassembly contact portion extends within the space between the armssubstantially from one arm to the other.

14. An electric switch comprising a switchblade mounted for rotationaround an axis of rotation, first contact means mounted so that aportion thereof substantially passes through the axis of rotation of theswitchblade, a contact portion formed on one end of the switchbladehaving an edge substantially coincident with the axis of rotation of theswitchblade, and second contact means displaced from the first contactmeans adapted to electrically communicate with a second contact portionformed on the other end of the switchblade.

15. A switch as defined in claim 14, wherein the second contact meanscomprises a contact assembly mounted for rotation about an axis ofrotation having a projecting contact edge formed thereon adapted toremain substantially coincident with the axis of rotation of the contactassembly, and stationary contact mem ber mounted so that a segmentthereof passes through the axis of rotation of the contact assembly.

1. An electric switch comprising, a movable electrical member mountedfor rotation around an axis of rotation, at least one stationaryterminal contact mounted so that a segment thereof lies substantiallyalong the axis of rotation of said movable member, said member having acontact portion formed on one end with an edge substantially coincidentwith the axis of rotation of said member said edge electrically engagingsaid stationary terminal contact segment.
 2. The switch recited in claim1, wherein the stationary terminal contact includes a U-shaped contactcomprising a pair of contact legs, one of said legs in a plane passingthrough the axis of rotation of the switchblade.
 3. The switch describedin claim 1, wherein the movable member contact portion includes an edgecoincident with the axis of rotation of the member and continuously incontact with the segment of the terminal contact which passes throughsaid axis of rotation.
 4. The switch recited in claim 1, wherein thestationary terminal contact includes a U-shaped contact which includes apair of contact legs having a spring disposed therebetween normallyurging the legs apart so that one of the legs is urged against saidcontact portion edge which is substantially coincident with the axis ofrotation of the movable member.
 5. The switch as recited in claim 1,wherein the stationary terminal contact includes a plurality of U-shapedterminal contacts, each contact member having a leg which substantiallypasses through the center of rotation of the movable member.
 6. Theswitch as recited in claim 1, wherein the contact portion is formed ofan electrically conductive material rigidly connected to the memberhaving an edge defined by a pair of surfaces meeting at an angle of 90*or less, the edge being substantially coincident with the axis ofrotation of the member.
 7. The switch of claim 1, wherein one end of themovable member is bifurcated to form a pair of spaced legs and thecontact portion of the movable member includes an electricallyconductive block rigidly connected to the member, the block extendingwithin the space between the legs substantially from one leg to theother.
 8. A switch terminal contact assembly comprising a contactassembly mounted for rotation about an axis of rotation, a contactportion formed on the contact assembly having an edge adapted to remainsubstantially coincident with the axis of rotation of the contactassembly during rotation thereof, and at least one stationary terminalcontact member mounted so that a segment thereof passes through the axisof rotation of the contact assembly.
 9. THe terminal assembly recited inclaim 8, wherein the terminal contact member includes a U-shaped contactcomprising a pair of contact legs, one of said legs passing through theaxis of rotation of the contact assembly.
 10. The terminal assemblyrecited in claim 8, wherein the contact assembly contact portionincludes a projection having an edge coincident with the assembly axisof rotation and continuously in electrical engagement with the segmentof the stationary contact member which passes through the assembly axisof rotation.
 11. The terminal assembly recited in claim 8, wherein thestationary terminal contact member includes a U-shaped contact formed ofa pair of contact legs having a spring disposed therebetween normallyurging the legs apart so that one of the legs is urged against said edgeof the contact assembly contact portion which is substantiallycoincident with the axis of rotation of the switchblade.
 12. Theterminal assembly defined in claim 8, wherein the contact assembly has asubstantially U-shaped frame and includes a pair of spaced parallel armsconnected by an electrically conductive bridging member, the parallelarms having mutually opposed electrical contacts fixed thereon and thebridging member having a rearwardly extending projection formed thereonterminating in said edge which is substantially coincident with thecenter of rotation of the contact assembly.
 13. The terminal assembly asdefined in claim 8, wherein a pair of spaced arms are provided on thecontact assembly and the contact assembly contact portion extends withinthe space between the arms substantially from one arm to the other. 14.An electric switch comprising a switchblade mounted for rotation aroundan axis of rotation, first contact means mounted so that a portionthereof substantially passes throuGh the axis of rotation of theswitchblade, a contact portion formed on one end of the switchbladehaving an edge substantially coincident with the axis of rotation of theswitchblade, and second contact means displaced from the first contactmeans adapted to electrically communicate with a second contact portionformed on the other end of the switchblade.
 15. A switch as defined inclaim 14, wherein the second contact means comprises a contact assemblymounted for rotation about an axis of rotation having a projectingcontact edge formed thereon adapted to remain substantially coincidentwith the axis of rotation of the contact assembly, and stationarycontact member mounted so that a segment thereof passes through the axisof rotation of the contact assembly.